View TC7660_70974.PDF datasheet online --- IC-ON-LINE

Datasheet File OCR Text:

EVALUATION KIT AVAILABLE
1
TC7660
CHARGE PUMP DC-TO-DC VOLTAGE CONVERTER
FEATURES
s s s s s s s s s s Converts +5V Logic Supply to 5V System Wide Input Voltage Range .................... 1.5V to 10V Efficient Voltage Conversion ......................... 99.9% Excellent Power Efficiency ............................... 98% Low Power Supply ...............................80A @ 5VIN Low Cost and Easy to Use -- Only Two External Capacitors Required RS232 Negative Power Supply Available in Small Outline (SO) Package Improved ESD Protection ....................... Up to 3kV No Dx Diode Required for High Voltage Operation
GENERAL DESCRIPTION
The TC7660 is a pin-compatible replacement for the Industry standard TC7660 charge pump voltage converter. It converts a +1.5V to +10V input to a corresponding - 1.5V to - 10V output using only two low-cost capacitors, eliminating inductors and their associated cost, size and EMI. The on-board oscillator operates at a nominal frequency of 10kHz. Operation below 10kHz (for lower supply current applications) is possible by connecting an external capacitor from OSC to ground (with pin 1 open). The TC7660 is available in both 8-pin DIP and 8-pin SOIC packages in commercial and extended temperature ranges.
2 3 4
Temperature Range
0C to +70C 0C to +70C - 40C to +85C - 40C to +85C - 40C to +85C - 55C to +125C
PIN CONFIGURATION (DIP and SOIC)
ORDERING INFORMATION
Part No. Package
8-Pin SOIC 8-Pin Plastic DIP 8-Pin SOIC 8-Pin Plastic DIP 8-Pin CerDIP 8-Pin CerDIP
NC
1
8 V+ 7 OSC
NC
1
8 V+ 7 OSC
TC7660COA TC7660CPA TC7660EOA TC7660EPA TC7660IJA TC7660MJA
CAP + 2 GND
CAP + 2 GND CAP - 3 4
3 TC7660CPA 6 LOW VOLTAGE (LV)
CAP - 4
TC7660EPA TC7660IJA 5 VOUT
TC7660COA 6 LOW VOLTAGE (LV) TC7660CPA
5 VOUT
5 6
NC = NO INTERNAL CONNECTION
TC7660EV
Evaluation Kit for Charge Pump Family
FUNCTIONAL BLOCK DIAGRAM
V + CAP + 8 2
OSC
7
RC OSCILLATOR
/2
VOLTAGE- LEVEL TRANSLATOR
4
CAP -
LV
6 5 INTERNAL VOLTAGE REGULATOR LOGIC NETWORK VOUT
7
TC7660
3 GND
8
TC7660-7 9/30/96
TELCOM SEMICONDUCTOR, INC.
4-51
CHARGE PUMP DC-TO-DC VOLTAGE CONVERTER TC7660
ABSOLUTE MAXIMUM RATINGS*
Supply Voltage ...................................................... +10.5V LV and OSC Inputs Voltage (Note 1) ........................ - 0.3V to (V+ + 0.3V) for V+ < 5.5V + - 5.5V) to (V+ + 0.3V) (V for V+ > 5.5V Current Into LV (Note 1) ..................... 20 A for V+ > 3.5V Output Short Duration (VSUPPLY 5.5V) ......... Continuous Power Dissipation (TA 70C) (Note 2) CerDIP ............................................................800mW Plastic DIP ......................................................730mW SOIC ...............................................................470mW Operating Temperature Range C Suffix .................................................. 0C to +70C I Suffix ............................................... - 25C to +85C E Suffix ............................................. - 40C to +85C M Suffix ........................................... - 55C to +125C Storage Temperature Range ................ - 65C to +150C Lead Temperature (Soldering, 10 sec) ................. +300C
*Static-sensitive device. Unused devices must be stored in conductive material. Protect devices from static discharge and static fields. Stresses above those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are stress ratings only and functional operation of the device at these or any other conditions above those indicated in the operation sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS: Specifications Measured Over Operating Temperature Range With,
V+ = 5V, COSC = 0, Test Circuit (Figure 1), unless otherwise indicated. Symbol
I+ V+H V+L ROUT
Parameter
Supply Current Supply Voltage Range, High Supply Voltage Range, Low Output Source Resistance
Test Conditions
RL = Min TA Max, RL = 10 k, LV Open Min TA Max, RL = 10 k, LV to GND IOUT = 20mA, TA = 25C IOUT = 20mA, 0C TA +70C (C Device) IOUT = 20mA, - 40C TA +85C (I Device) IOUT = 20mA, - 55C TA +125C (M Device) V+ = 2V, IOUT = 3 mA, LV to GND 0C TA +70C V+ = 2V, IOUT = 3 mA, LV to GND - 55C TA +125C (Note 3) Pin 7 open RL = 5 k RL = V+ = 2V V+ = 5V
Min
-- 3 1.5 -- -- -- -- -- -- -- 95 97 -- --
Typ
80 -- -- 70 -- -- 104 150 160 10 98 99.9 1 100
Max
180 10 3.5 100 120 130 150 300 600 -- -- -- -- --
Unit
A V V kHz % % M k
FOSC PEFF VOUT EFF ZOSC
Oscillator Frequency Power Efficiency Voltage Conversion Efficiency Oscillator Impedance
NOTES: 1. Connecting any input terminal to voltages greater than V+ or less than GND may cause destructive latch-up. It is recommended that no inputs from sources operating from external supplies be applied prior to "power up" of the TC7660. 2. Derate linearly above 50C by 5.5 mW/C. 3. TC7660M only. 4. The TC7660 can be operated without the Dx diode over full temperature and voltage range.
4-52
TELCOM SEMICONDUCTOR, INC.
CHARGE PUMP DC-TO-DC VOLTAGE CONVERTER TC7660
TYPICAL PERFORMANCE CHARACTERISTICS (Circuit of Figure 1)
Operating Voltage vs. Temperature
POWER CONVERSION EFFICIENCY (%)
1
Power Conversion Eff. vs. Osc. Freq.
100 98 96 94 92 90 88 86 84 82 TA = +25C V+ = +5V 1k OSCILLATOR FREQUENCY (Hz) 10k IOUT = 15 mA IOUT = 1 mA
12 10
SUPPLY VOLTAGE (V)
2 3 4 5
8 6 4 2 SUPPLY VOLTAGE RANGE
0 -55
-25
0 +25 +50 +75 +100 +125 TEMPERATURE (C)
80 100
Output Source Resistance vs. Supply Voltage
10k
OUTPUT SOURCE RESISTANCE ()
Output Source Resistance vs. Temperature
500
OUTPUT SOURCE RESISTANCE ()
TA = +25C
IOUT = 1 mA 450 400 200 150 V + = +2V 100 50 V + = +5V
1k
100
10 0 1 2 3 4 5 6 SUPPLY VOLTAGE (V) 7 8
0 -55
-25
0 +25 +50 +75 +100 +125 TEMPERATURE (C)
6 7
Freq. of Osc. vs. Ext. Osc. Capacitance
10k
OSCILLATOR FREQUENCY (Hz)
Unloaded Osc. Freq. vs. Temperature
20
OSCILLATOR FREQUENCY (kHz)
TA = +25C V+ = +5V
V+ = +5V
18 16 14 12 10 8 6 -55
1k
100
10 1 10 100 1000 OSCILLATOR CAPACITANCE (pF) 10k
-25
0 +25 +50 +75 +100 +125 TEMPERATURE (C)
8
4-53
TELCOM SEMICONDUCTOR, INC.
CHARGE PUMP DC-TO-DC VOLTAGE CONVERTER TC7660
TYPICAL CHARACTERISTICS (Cont.)
Output Voltage vs. Output Current
0 -1 5 4 3 TA = +25C V+ = +5V
Output Voltage vs. Load Current
OUTPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
TA = +25C LV OPEN 0 10 20 30 40 50 60 70 80 90 100 OUTPUT CURRENT (mA)
-2 -3 -4 -5 -6 -7 -8 -9 -10
2 1 0 -1 -2 -3 -4 -5 0 10 20 30 40 50 60 70 LOAD CURRENT (mA) 80 SLOPE 55
Supply Current and Power Conversion Efficiency vs. Load Current
POWER CONVERSION EFFICIENCY (%)
90 80 70 60 50 40 30 20 10 0 1.5 3.0 4.5 6.0 7.5 LOAD CURRENT (mA) TA = +25C V+ = 2V
POWER CONVERSION EFFICIENCY (%)
100
20
100 90 80 70 60 50 40 30 20 10 0 10 TA = +25C V+ = +5V 20 30 40 50 LOAD CURRENT (mA) 60
100
SUPPLY CURRENT (mA) (Note)
16 14 12 10 8 6 4 2 0 9.0
80 70 60 50 40 30 20 10 0
Output Voltage vs. Load Current
2 TA = +25C V+ = +2V
OUTPUT VOLTAGE (V)
1
0
-1
SLOPE 150 -2 0 1 2 3 4 5 6 LOAD CURRENT (mA) 7 8
4-54
TELCOM SEMICONDUCTOR, INC.
SUPPLY CURRENT (mA) (Note)
18
90
CHARGE PUMP DC-TO-DC VOLTAGE CONVERTER TC7660
The four switches in Figure 2 are MOS power switches; S1 is a P-channel device, and S2, S3 and S4 are N-channel devices. The main difficulty with this approach is that in integrating the switches, the substrates of S3 and S4 must always remain reverse-biased with respect to their sources, but not so much as to degrade their ON resistances. In addition, at circuit start-up, and under output short circuit conditions (VOUT = V+), the output voltage must be sensed and the substrate bias adjusted accordingly. Failure to accomplish this will result in high power losses and probable device latch-up. This problem is eliminated in the TC7660 by a logic network which senses the output voltage (VOUT) together with the level translators, and switches the substrates of S3 and S4 to the correct level to maintain necessary reverse bias. The voltage regulator portion of the TC7660 is an integral part of the anti-latch-up circuitry. Its inherent voltage drop can, however, degrade operation at low voltages. To improve low-voltage operation, the LV pin should be connected to GND, disabling the regulator. For supply voltages greater than 3.5V, the LV terminal must be left open to ensure latch-up-proof operation and prevent device damage.
1
IS 1 2 C1 10F + 3 4 8 7 IL V+ (+5V)
2 3 4 5 6 7
TC7660
6 5
COSC*
RL VO C2 10F
+
NOTES: * For large values of COSC (>1000pF), the values of C1 and C2 should be increased to 100F.
Figure 1. TC7660 Test Circuit
Detailed Description
The TC7660 contains all the necessary circuitry to implement a voltage inverter, with the exception of two external capacitors, which may be inexpensive 10 F polarized electrolytic capacitors. Operation is best understood by considering Figure 2, which shows an idealized voltage inverter. Capacitor C1 is charged to a voltage, V+, for the half cycle when switches S1 and S3 are closed. (Note: Switches S2 and S4 are open during this half cycle.) During the second half cycle of operation, switches S2 and S4 are closed, with S1 and S3 open, thereby shifting capacitor C1 negatively by V+ volts. Charge is then transferred from C1 to C2, such that the voltage on C2 is exactly V+, assuming ideal switches and no load on C2.
Theoretical Power Efficiency Considerations
In theory, a capacitive charge pump can approach 100% efficiency if certain conditions are met: (1) The drive circuitry consumes minimal power. (2) The output switches have extremely low ON resistance and virtually no offset. (3) The impedances of the pump and reservoir capacitors are negligible at the pump frequency.
V+
S1
S2
GND
S3
S4
C2 VOUT = - VIN
Figure 2. Idealized Charge Pump Inverter
8
4-55
TELCOM SEMICONDUCTOR, INC.
CHARGE PUMP DC-TO-DC VOLTAGE CONVERTER TC7660
The TC7660 approaches these conditions for negative voltage multiplication if large values of C1 and C2 are used. Energy is lost only in the transfer of charge between capacitors if a change in voltage occurs. The energy lost is defined by: E = 1/2 C1 (V12 - V22) V1 and V2 are the voltages on C1 during the pump and transfer cycles. If the impedances of C1 and C2 are relatively high at the pump frequency (refer to Figure 2), compared to the value of RL, there will be a substantial difference in voltages V1 and V2. Therefore, it is not only desirable to make C2 as large as possible to eliminate output voltage ripple, but also to employ a correspondingly large value for C1 in order to achieve maximum efficiency of operation. The output characteristics of the circuit in Figure 3 are those of a nearly ideal voltage source in series with 70. Thus, for a load current of - 10mA and a supply voltage of +5V, the output voltage would be - 4.3V. The dynamic output impedance of the TC7660 is due, primarily, to capacitive reactance of the charge transfer capacitor (C1). Since this capacitor is connected to the output for only 1/2 of the cycle, the equation is: 2 XC = 2f C1 = 3.18, where f = 10kHz and C1 = 10F.
V
+
Dos and Don'ts
* Do not exceed maximum supply voltages. * Do not connect LV terminal to GND for supply voltages greater than 3.5V. * Do not short circuit the output to V supply for voltages above 5.5V for extended periods; however, transient conditions including start-up are okay. * When using polarized capacitors in the inverting mode, the + terminal of C1 must be connected to pin 2 of the TC7660 and the + terminal of C2 must be connected to GND Pin 3.
+
1 C1 10F + 2 3 4
8 7 VOUT* C2 10F
TC7660
6 5
+
* NOTES:
1. VOUT = -n V+ for 1.5V V+ 10V
Figure 3. Simple Negative Converter
Simple Negative Voltage Converter
Figure 3 shows typical connections to provide a negative supply where a positive supply is available. A similar scheme may be employed for supply voltages anywhere in the operating range of +1.5V to +10V, keeping in mind that pin 6 (LV) is tied to the supply negative (GND) only for supply voltages below 3.5V.
Paralleling Devices
Any number of TC7660 voltage converters may be paralleled to reduce output resistance (Figure 4). The reservoir capacitor, C2, serves all devices, while each device requires its own pump capacitor, C1. The resultant output resistance would be approximately: ROUT = ROUT (of TC7660) n (number of devices)
4-56
TELCOM SEMICONDUCTOR, INC.
CHARGE PUMP DC-TO-DC VOLTAGE CONVERTER TC7660
V+ 1 2 C1 3 4 8 7 1 2 C1 3 4 8 7 RL
1
2
TC7660
"n" 6 5
TC7660
"1"
6 5
+
Figure 4. Paralleling Devices Lowers Output Impedance
C2
3 4 5 6 7
VOUT*
Cascading Devices
The TC7660 may be cascaded as shown (Figure 6) to produce larger negative multiplication of the initial supply voltage. However, due to the finite efficiency of each device, the practical limit is 10 devices for light loads. The output voltage is defined by: VOUT = -n (VIN) where n is an integer representing the number of devices cascaded. The resulting output resistance would be approximately the weighted sum of the individual TC7660 ROUT values.
Changing the TC7660 Oscillator Frequency
It may be desirable in some applications (due to noise or other considerations) to increase the oscillator frequency. This is achieved by overdriving the oscillator from an external clock, as shown in Figure 6. In order to prevent possible
V 1 2 + 10F 3 4 8 7 +
device latch-up, a 1k resistor must be used in series with the clock output. In a situation where the designer has generated the external clock frequency using TTL logic, the addition of a 10k pull-up resistor to V+ supply is required. Note that the pump frequency with external clocking, as with internal clocking, will be 1/2 of the clock frequency. Output transitions occur on the positive-going edge of the clock. It is also possible to increase the conversion efficiency of the TC7660 at low load levels by lowering the oscillator frequency. This reduces the switching losses, and is achieved by connecting an additional capacitor, COSC, as shown in Figure 7. Lowering the oscillator frequency will cause an undesirable increase in the impedance of the pump (C1) and the reservoir (C2) capacitors. To overcome this, increase the values of C1 and C2 by the same factor that the frequency has been reduced. For example, the addition of a 100pF capacitor between pin 7 (OSC) and pin 8 (V+) will lower the oscillator frequency to 1kHz from its nominal frequency of 10kHz (a multiple of 10), and necessitate a corresponding increase in the values of C1 and C2 (from 10F to 100F).
1 2 + 10F 3 4
8 7
TC7660
"1"
6 5
TC7660
"n"
6 5 +
10F
* NOTES:
1. VOUT = -n V + for 1.5V V + 10V
Figure 5. Increased Output Voltage by Cascading Devices
8
4-57
TELCOM SEMICONDUCTOR, INC.
CHARGE PUMP DC-TO-DC VOLTAGE CONVERTER TC7660
V+ 1 2 + 10F 3 4 8 1 k 7 CMOS GATE V+
Combined Negative Voltage Conversion and Positive Supply Multiplication
Figure 9 combines the functions shown in Figures 3 and 8 to provide negative voltage conversion and positive voltage multiplication simultaneously. This approach would be, for example, suitable for generating +9V and -5V from an existing +5V supply. In this instance, capacitors C1 and C3 perform the pump and reservoir functions, respectively, for the generation of the negative voltage, while capacitors C2 and C4 are pump and reservoir, respectively, for the multiplied positive voltage. There is a penalty in this configuration which combines both functions, however, in that the source impedances of the generated supplies will be somewhat higher due to the finite impedance of the common charge pump driver at pin 2 of the device.
TC7660
6 5 + 10F VOUT
Figure 6. External Clocking V+ 1 2 C1 + 3 4 8 7 COSC
TC7660
6 5 + C2
1 8 7 +
VOUT
V+
VOUT = - (V+- VF) C3
Figure 7. Lowering Oscillator Frequency
2 3 + C1 4 + C2
Positive Voltage Multiplication
The TC7660 may be employed to achieve positive voltage multiplication using the circuit shown in Figure 8. In this application, the pump inverter switches of the TC7660 are used to charge C1 to a voltage level of V+- VF (where V+ is the supply voltage and VF is the forward voltage drop of diode D1). On the transfer cycle, the voltage on C1 plus the supply voltage (V+) is applied through diode D2 to capacitor C2. The voltage thus created on C2 becomes (2 V+) - (2 VF), or twice the supply voltage minus the combined forward voltage drops of diodes D1 and D2. The source impedance of the output (VOUT) will depend on the output current, but for V+ = 5V and an output current of 10 mA, it will be approximately 60.
V+ 1 2 3 4 8 7 D1 D2 + C1 + C2 VOUT = (2 V+) - (2 VF)
TC7660
6 5
D1
D2
VOUT = (2 V +) - (2 VF) + C4
Figure 9. Combined Negative Converter and Positive Multiplier
Efficient Positive Voltage Multiplication/Conversion
Since the switches that allow the charge pumping operation are bidirectional, the charge transfer can be performed backwards as easily as forwards. Figure 10 shows a TC7660 transforming -5V to +5V (or +5V to +10V, etc.). The only problem here is that the internal clock and switchdrive section will not operate until some positive voltage has been generated. An initial inefficient pump, as shown in Figure 9, could be used to start this circuit up, after which it will bypass the other (D1 and D2 in Figure 9 would never turn on), or else the diode and resistor shown dotted in Figure 10 can be used to "force" the internal regulator on.
TC7660
6 5
Figure 8. Positive Voltage Multiplier 4-58
TELCOM SEMICONDUCTOR, INC.
CHARGE PUMP DC-TO-DC VOLTAGE CONVERTER TC7660
VOUT = -V-
+ R L1 50 F V +
1
1 2 C1 10F + 3 4
8 7 1 M
1 2
8 7
1 M
2 3 4 5 6 7
+
10F
V
TC7660
6 5 V- INPUT
= OUT + - V -V 2
50 F + - 100 k
3 4
TC7660
6 5
R L2
+ 50 F - V -
Figure 10. Positive Voltage Conversion
Figure 11. Splitting a Supply in Half
Voltage Splitting
The same bidirectional characteristics used in Figure 10 can also be used to split a higher supply in half, as shown in Figure 11. The combined load will be evenly shared between the two sides. Once again, a high value resistor to the LV pin ensures start-up. Because the switches share the load in parallel, the output impedance is much lower than in the standard circuits, and higher currents can be drawn from the device. By using this circuit, and then the circuit of Figure 5, +15V can be converted (via +7.5V and -7.5V) to a nominal -15V, though with rather high series resistance (~250).
8
TELCOM SEMICONDUCTOR, INC.
4-59

▲Up To Search▲

Price & Availability of TC7660

	To Download TC7660 Datasheet File
If you can't view the Datasheet, Please click here to try to view without PDF Reader .